The present invention relates to a bubble-dispersing apparatus for dispersing a large quantity of bubbles in a tank containing a fluid while maintaining said fluid contained in the tank a stationary state, which apparatus is suitable for use in the flotation/separation operation for substances having a relatively small specific gravity, particularly in the case of the sorting of waste plastics or the de-inking of wastepaper.
As the generally known art of separating and recovering a specific solid from a fluid containing various solids mixed therein, there is an art of effecting flotation/separation by taking advantage of the fact that different kinds of solids have different bubble adsorption functions according to the properties of the surfaces of solids so that one solid can be floated and separated from other solids by virtue of the buoyancy of the bubbles. As this art utilizes the adsorbancy of bubbles to the surface of solids as stated above, it is necessary to prevent, as far as possible, the occurrence of a dynamic state of the fluid, such as flowing, oscillation or vibration of the fluid, which constitutes a main obstruction to the adsorption of bubbles to the surfaces of solids or separation of bubbles from the surfaces of solids after they have been adsorbed thereto. Accordingly, the extent to which the fluid can be maintained in a stationary state under the condition of effecting the dispersion of bubbles constitutes an essential point in determining the exactitude of a flotation/separation operation.
To cite a conventional apparatus devised by applying the foregoing art of effecting flotation/separation, there is the apparatus for the purpose of sorting ores having a relatively great specific gravity.
In the case of this apparatus too, it is desirable to maintain the fluid admixed with various solids within the tank in a stationary state as far as possible. But because ores having greater specific gravity are apt to precipitate and to be deposited on the bottom of the tank, the apparatus is devised to stir the fluid intensely at the sacrifice of maintaining the stationary state of the fluid to some extent in order to maintain said ores in a floating state within the fluid. On the other hand, in the case of effecting separation/flotation of substances having a relatively small specific gravity such as those mentioned above, there is little fear of precipitation of the object substances and stirring of the fluid is not particularly required, and accordingly, the influence of the bubble-dispersing apparatus per se on the fluid is very important, so that the construction of the apparatus is required to be such that it will not impair the stationary state of the fluid as far as possible, and especially it will not disturb the stationary state in the forth layer formed on the surface of fluid as well as in the bubble-ascending zone extending from the lower part of the tank to said surface of the fluid.
However, there has not yet been developed any suitable apparatus for the purpose of dispersing bubbles under a fluid in such conditions as discussed above.
Under such circumstances, the principal object of the present invention is to provide a bubble-dispersing apparatus which will exactly meet the foregoing requirements.
Another object of the present invention is to provide a bubble-dispersing apparatus, which comprises a tank for containing a fluid, a vertical rotary shaft installed in said tank and connected with a power source, a fixing plate installed on the lower part of said rotary shaft and extending perpendicular thereto, stirring blades installed on the bottom face of said fixing plate, plural radially disposed guide blades surrounding the rotation zone of said stirring blades and located practically on the same horizontal level as that of said stirring blades by means of a frame whose top is closed, and a gas supply pipe installed beneath and in confronting relationship to said stirring blades, whereby a gas supplied to the tank through said gas supply pipe while rotating said stirring blades can be split into bubbles with relatively small diameters, further split into bubbles with lesser diameter by the shearing force generated between the stirring blades and the guide blades and dispersed radially and uniformly in the tank through the guide blades, while the fluid that flows out radially from the guide blades into the ascending zone circulates along with the ascending current of fluid generated by the pumping action of the stirring blades together with the gas being blown out of the gas supply pipe, and the kinetic energy thereof is absorbed and consumed while thus circulating, so that no influence of the current of fluid is exerted upon the upper part of tank and the stationary state of the fluid thereat can be maintained.
A further object of the present invention is to provide a bubble-dispersing apparatus, which comprises a solid-dispersing mechanism consisting of a vertical rotary shaft installed in a tank for containing a fluid and connected with a power source, a fixing plate installed on the lower part of said rotary shaft and extending perpendicular thereto, stirring blades installed on the top face of said fixing plate, plural radially disposed guide blades surrounding the rotation zone of said stirring blades and located practically on the same horizontal level as that of said stirring blades by means of a frame, and a solid supply pipe installed above said stirring blades so as to be in front thereof, and a bubble-dispersing mechanism disposed beneath said solid-dispersing mechanism and consisting of a fixing plate installed on the same rotary shaft and extending perpendicular thereto, stirring blades installed on the bottom face of said fixing plate, plural radially disposed guide blades surrounding the rotation zone of said stirring blades and located practically on the same horizontal level as that of the stirring blades by means of the frame, and a gas supply pipe installed beneath and in confronting relationship to said stirring blades, whereby a gas supplied to the tank through said gas supply pipe while rotating said stirring blades can be first split into bubbles with relatively small diameters, further split into bubbles with lesser diameters by the shearing force generated between the stirring blades and the guide blades and dispersed radially and uniformly in the tank along with the fluid through the guide blades, and said bubbles are separated from the current of fluid and ascend in the tank, while the current of fluid comes to circulate by virtue of the pumping action pursuant to the rotation of the stirring blades as well as the ascending current of fluid generated by the gas being blown out of the gas supply pipe, and the kinetic energy of fluid is absorbed in the surroundings of the stirring blades so that not influence is exerted upon the fluid in the upper part of the tank, and solids are automatically taken into the tank through the solid supply pipe by the sucking action pursuant to the rotation of the solid-stirring blades, are dispersed uniformly in the tank by means of said stirring blades as well as solid guide blades, collide with bubbles ascending from beneath and absorb them onto their surface, thereby to make a specified solid float and separate from other solids.